It has previously been proposed to prepare highly swelling polymers from unsaturated carboxylic compounds such as maleic anhydride by polymerizing the carboxylic monomer with a cross-linking agent such as a polyethylenically unsaturated compound as shown in U.S. Pat. No. 2,798,053 and references cited therein. Such polymers have been employed as synthetic gums to produce mucilaginous or gel-like aqueous compositions.
It has further been suggested to employ solid linear copolymers of maleic anhydride and styrene in admixture with a substantial proportion of polyhydric alcohol, as for example in U.S. Pat. No. 3,085,986, to produce thermoset molded resins wherein the final product is cross-linked by reaction of the polyhydric alcohol with the anhydride residues in the linear polymer. The products from this latter procedure are hard resins which absorb only minimal amounts of water or sodium chloride solution even after immersion therein for 7 days.
It has recently been suggested, for example in British Pat. No. 1,200,106, that certain lightly cross-linked polymers containing a plurality of hydrophilic units can advantageously be employed to absorb and bind body fluids. Such polymers, typically lightly cross-linked, partially hydrolyzed polyacrylamides, are recommended as constituents of the filler of disposable diapers, bed pads and other such sanitary products by reason of their ability to hold substantially more aqueous fluid under pressure than can be held by an equal weight of cellulosic fluff or the like. However, in certain applications of such highly water-swellable polymers, difficulties have been encountered in confining the polymer after it becomes engorged with aqueous fluid.
It would be desirable to have a highly water-swellable water-insoluble polymer in fiber form. Such a material would lend itself to incorporation in woven or nonwoven fabrics either alone or together with conventional synthetic or natural fibers. Such a material could also be handled by conventional mechanical devices for fabricating disposable diapers and the like. Further, such water-swellable fibers could be more easily confined in a sanitary product either when dry or when engorged with aqueous fluid. However, when water-swellable polymers are prepared in the usual fashion by incorporating the cross-linking agent during the polymerization reaction by which said polymer is formed, the resulting cross-linked polymer product generally cannot be fabricated into fibers or filaments by conventional methods.